Cruise control systems are known for motor vehicles for regulating the speed of the vehicle at a desired speed selected by the driver. If the vehicle also has a distance sensor, e.g., in the form of a radar sensor, a stereo camera system or the like, the vehicle speed may also be regulated in such a way that a suitable safety distance from a vehicle traveling in front is automatically maintained. One example of such a regulating system, which is also known as an ACC system (active cruise control), is described in “Adaptive Cruise Control System—Aspects and Development Trends” by Winner, Witte, Uhler and Lichtenberg, Robert Bosch GmbH, in SAE Technical Paper Series 961010, International Congress & Exposition, Detroit, Feb. 26–29, 1996.
The switch with which the driver is able to change the desired speed is usually formed by a lever on the steering wheel, which is movable either up or down to increase or reduce the desired speed. If this lever is kept in the upper end position for a long period of time, the determination device causes an incremental increase in the desired speed with fixed increments and at fixed intervals. Accordingly, the desired speed is reduced when the driver keeps the lever in the lower position. When the driver releases the lever, the set desired speed is maintained.
With the help of the accelerator pedal or, more generally, with the help of an acceleration control device, the driver may also intervene directly in the driving system of the vehicle and thus override the function of the cruise control system at any time. Thus, for example, the driver may depress the accelerator pedal to temporarily exceed the set desired speed so as to pass another vehicle. When the driver releases the accelerator pedal again, the speed of the vehicle drops back to the previously set desired speed. However, when the driver has accelerated the vehicle with the help of the accelerator pedal, the driver may briefly tip the lever up or down so that the vehicle speed which has then been reached will be stored as the new desired speed. In this sense, the acceleration control device, i.e., the accelerator pedal is also to be regarded as part of the input device.
German Published Patent Application No. 198 02 704 describes an input device using which the desired speed may be varied only incrementally, e.g., in 10 km/h increments. If the driver operates the switch while accelerating by using the accelerator pedal, the value closest to the actual speed then reached is stored as the new desired speed.
In general the driver thus has two possibilities of increasing the desired speed. First, the driver may accelerate the vehicle with the help of the accelerator pedal and then set the new desired speed by touching the switch. Second, the driver may hold the lever in the top position to cause the determination device to increase the desired speed at a fixedly predetermined rate of increase.
The advantage of the first variant is that the driver himself is able to determine by the pressure on the accelerator pedal at what rate the vehicle is accelerated, so that the driver is able to reach the new desired speed relatively rapidly by a high rate of acceleration of the vehicle. However, one disadvantage is that the new desired speed may not be set until the vehicle has reached that speed. Since the regulating system operates with an unavoidable control lag, this may result in temporary overshooting of the actual desired speed.
This overshooting of the regulating system may be largely avoided with the second variant. Another advantage of this variant is that the change in the throttle valve setting and/or the injection quantity using which the acceleration of the vehicle is induced is not determined directly by the driver in this case but instead is calculated by the engine management system of the vehicle and therefore may be optimally adapted to the particular operating state of the engine, so that acceleration is accomplished with optimum efficiency and therefore with favorable fuel consumption. One disadvantage of the second variant, however, is that the driver must hold the lever in the upper position until the setting ultimately desired has been reached by incrementally increasing the desired speed. This is perceived in a negative sense in terms of comfort and may also result in negative effects on driving safety, in particular when negotiating turns at a high speed. Even if the lever is located near the steering wheel, the driver will be unable to grip the steering wheel firmly with two hands as long as he is operating the lever, so this has a negative effect on control over the steering.
The time required for setting the higher desired speed depends on the increments and intervals by which the speed is increased as the desired speed is being implemented by the determination device. When the increments are larger, the new desired speed may be achieved rapidly, but with a relatively low precision. Conversely, if the desired speed is increased in shorter intervals, setting the speed is more difficult because of the very critical dependence of the desired speed on the duration of operation of the lever. When there is a rapid increase in the desired speed, the actual speed also remains temporarily behind the desired speed, so the driver may inadvertently set a desired speed that is too high and then have to correct the desired speed subsequently by adjusting it back in the opposite direction.